Communication systems have become more sophisticated and advanced over the past several decades. For example, many traditional communication devices utilized only a single microphone to sense sound from either a near-end or a far-end user. These more basic systems experience echo. For the far-end system this is caused by the pickup of monophonic sound which originates from the near-end user that is played through a far-end system's loudspeaker or loudspeakers. The monophonic nature of the echo, either due to the monophonic nature of the near-end source and/or playback over only one loudspeaker on the far-end system, often means this echo can be efficiently controlled through the use of a dedicated monophonic echo canceller assigned to the far-end microphone, or each of the far-end microphones or beams.
Similarly, if the echo is monophonic in nature at the near-end user, either due to the monophonic nature of the far-end source and/or playback over only one loudspeaker by the near-end system, the near-end system can often efficiently cancel echo using a monophonic echo canceller.
However, many modern systems may generate multiple channels of audio corresponding to separate areas of the near-end. Examples include the use of multiple microphones, different beamformers, and even addition of other sources into the channels such as recorded music or audio from games or movies.
In addition, many modern systems have the ability to use more than one loudspeaker. Thus, in scenarios where the playback of such multiple channels is done over multiple loudspeakers the nature of the echo is often not monophonic, but multi-channel. This requires use of a multi-channel echo canceller to cancel echo.
Multi-channel echo cancellers have a number of challenges that monophonic echo cancellers do not. One of these challenges is due to the nature of the multi-channel sources that are then played over the loudspeaker. For example, due to the nature of many multi-channel pick up systems, and the environment they operate in, the multiple channels may be highly correlated. This high correlation between channels may result in a multi-channel echo canceller not being able to accurately estimate echo paths corresponding to the different channels. This is a situation of misalignment in channel estimates that results in poor stereo acoustic echo cancellation.
One solution to mitigate this problem is to modify the multiple channels so that there is less inter-channel correlation. This is the technique of decorrelation, often implemented in the playback system. Although de-correlation techniques may be used to assist in stereo acoustic echo cancellation, these “downlink” de-correlation techniques often entail non-linear modifications to individual channels, and thus may introduce artifacts into the signals. They may even dramatically change the nature of critical sounds (e.g., musical instruments).
These downlink decorrelation techniques (e.g., the far-end system would apply decorrelation in its own “downlink” playback system in order to assist in its own multi-channel echo cancellation) are reactive systems that can only work using the available channels that have been received by from the far-end device. They are thus more reactive in nature.
Further, in some cases, de-correlation may not always be appropriate. Accordingly, systems that uniformly/automatically apply de-correlation to one or more channels may be doing so unnecessarily.
In addition, there is information that the near-end system has that the far-end system does not have, which may aid in decorrelation for helping the far-end (e.g., the near-end often has more channels available to it that are not transmitted to the far-end).
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.